I don't know- a good lover can compensate pretty easily for either too big or too small. For instance, a guy with a true micropenis can easily still be an amazing lover if he's good with is hands and mouth and doesn't have a chip on his shoulder. A dude with an enormous penis can work with any woman's anatomy- if he's gentle and patient. That being said, I have a hard time imagining being so cruel as to kick a man out of bed for a small unit, but I damn well have backed the fuck out when faced with an enormous dick. (Good decision too for a 15 yo virgin in bed with another 15 yo virgin). As far as preferences go and what sizes are extreme enough that they require special effort or compensation? I guess under 4" and thin would be small enough that I doubt I'd be able to climax from intercourse alone. Anything probably over about 7" is going to bottom out (ouch!) on me before I orgasm, and I guess 8-9" is still going to bottom out even after I cum. Girth is less problematic- anything is doable, though it may take time and patience to acclimate.